Carbon mineralization kinetics in soils under urban environment.

In a short-term laboratory study, carbon mineralization potentials were determined on samples obtained from some representative urban soils located in Pisa (Tuscany, Italy). All the kinetic models tested to describe the mineralization process fitted well to the experimental data. The special model, a modified double exponential model combining first-order mineralization with zero order mineralization, best described the C mineralization of the urban soils. The low variability of rate constants suggests that urban soils of Pisa have similar easily mineralizable organic compounds or the same degree of availability. The parameters calculated according to the special model allowed the detection of a pool of easily biodegradable organic compounds (on average 0.75% of the total organic C of soils) which was exhausted in a very short period. Soil texture was found to influence the rate of the first phase of C mineralization. The mineralization first-order rate constants of the easily mineralizable C (k) were positively correlated with the sand contents, while high clay and silt contents were found to be indicative of low k.The mineralization parameters Cm (cumulative C mineralized after 25 days of incubation), C1 (easily mineralizable C) and h (time constant for the slowly mineralizable C) were found to be positively correlated with the organic C contents and negatively related to soil pH.